Jet propellant



.of the Venturi type.

United States Patent JET PROPELLANT Charles A. Thomas, Dayton, Ohio,assignor to Monsanto Chemical Company, St. Louis, Mo., a corporation ofDelaware N Drawing. Application August 22, 1945 Serial No. 612,133

6 Claims. (Cl. 52--.5)

The present invention relates generally to impulse generatingcompositions and more particularly to compositions suitable for theproduction of a high velocity gas jet, the reactive impulse of which maybe employed to perform useful work such as the propulsion of rocketshells (including anti-aircraft or anti-tank projectiles) or inassisting the take-off of airplanes, gliders, accelerating the movementof wheeled vehicles, etc.

Compositions of the type described herein are generally employed as agas generating fuel in a chamber referred to herein as a motor and whichusually consists of a cylindrical fuel chamber closed at one end andprovided at the opposite end with a coaxial orificeor throat The chamberis so constructed as to be. capable of withstanding the high gaspressure which is developed by combustion of the fuel. The products ofcombustion of the fuel issue as a high velocity gas jet through thethroat of the motor, the reactive effect of the gas creating thepropelling impulse employed in rocket or jet propulsion.

When motors of the foregoing type are employed in the propulsion ofartillery shells such as anti-tank or anti-aircraft shells the motorcontaining the propellant is generally attached to the base of theshell, the whole assembly being fired from a smooth-bore tube or rack.For use in assisting the take off of aircraft or accelerating the motionof vehicles generally, one or more of the motors may be mounted upon theplane or vehicle in such a way that the impulse created by the highvelocity gas jet is transmitted directly to the aircraft or vehicle.

The present compositions are adaptable to a wide variety of purposes,depending upon the rapidity and conditions under which they are burned.They may be adapted to the propulsion of artillery shells, in which casethe burning time is relatively short. They may also be adapted forassisting the take-off of airplanes either from land or water, in whichcase the burning time is considerably lengthened. In other cases theymay be used to assist in starting or accelerating the motion of vehiclessuch as railroad trains, in which case the burning time is stillsomewhat longer. By a suitable variation in the composition, as will behereinafter more fully described, impulse generating compositionssuitable for these various purposes may be produced.

In determining the suitability of any gas generating composition forimpulse, rocket or jet propulsion purposes, the most importantproperties of the fuel to be considered are: (1) its specific impulse,(2) the reproducibility of its burning properties, and (3) the relationbetween its rate of burning, the pressure and the temperature. Thespecific impulse is the total impulse (i. e., force-time integral)imparted to the motor per unit weight of propellant consumed andprovides a measure of the performance to be expected from a motor orrocket using the fuel in question. Reproducibility is indispensable ifpower and freedom from bursts are to be obtained; while a low depedenceof rate of burning on pressure and preignition temperature greatly sim-2 plifies motor design, increases the range of climatic conditions underwhich the device is usable and decreases the hazards which arise fromsmall variations in the property of the fuel.

The foregoing critical properties are all fundamentally related to therate of burning of the fuel and this, in turn is known to be dependentupon (1) the burning area of the fuel, (2) the pressure within the motorand (3) the pre-ignition temperature of the fuel. Considering firstlythe burning area factor, it is known that the rate of burning will varyif the burning area of the fuel as it is consumed is either decreasing(called a degressive or regressive burning area) or increasing (called aprogressive burning area).- The effect of this factor may be minimizedto a considerable extent by forming the composition into'bodies (calledgr-ains) having geometric forms so designed and inhibited as to insure asubstantially constant burningarea as the fuel is consumed.

Considering now the efiect of pressure on the burning rate, fromtheoretical considerations, it will be apparent that when the fuel isignited, the pressure within the motor chamber rises from atmosphericpressure to a higher pressure at a steady state. Inasmuch as thepressure existing within the rocket motor greatly affects the burningrate, erraticbehavior likely to result in explosions of the fuel chambermay be anticipated if the fuel is characterized by a pronounceddepedence of burning rate upon pressure. Considering the burningphenomena in greater details, after ignition of the fuel, the pressurewithin the motor chamber will rise until the rate of gas formationwithin the chamber equals thev rate of efilux, at which point a steadycondition will be attained. Since the rate of gaseous combustion products is proportional to the burning area of the grain (A and also tosome power of the pressure (P and since the rate of efilux isproportional to the pressure P and to the area of the orifice or throat(A a steady state will exist when:

K A P =K A P the steady state pressure is therefore given by:

A z ia) since P A and A, are all readily measurable quantities,

v it is possible to plot log P against log (A /A Such a plot willdescribe a straight line of the slope-intercept form, the slope of theline being the exponent 1/ (l-n), from which the value of theexponential constant n may be determined.

In the case of actual propellants, some deviation from the so-calledburning law may be observed. However, the smaller the average deviationof the observed pressures from a smooth plot of pressure against A /Athe more highly reproducible will be the internal ballistics 0f thefuel. Moreover, the closer the value of n approaches zero, the lesssensitive'does the system become to small variations in A and A i. e.,the less rapidly will the pressure vary with small variations'in thecondi tlons of burning such as the grain area, obstructions in r thethroat of the motor, etc. Conversely, the closer the .value of itapproaches unit,.the,more, sensitive does the system become tovariations in grain area and throat area, and in the limiting case wheren becomes unity, it will beapparent that the" pressurevariesas theinfinite power ofthe Agyto At ratio.-l r

Thus the swcalled burning: lawg and particularly the value of n, theexponential constant, are of fundamental importance 1 in? the selectionof a rocket propellant and inEthe design-of' the rocket motoryafuel-thabdeviates only slightly from the so-called' burning, law andthatpus-- sesses-a W" value of: n will-be characterized by a' high:reproducibilityof chamber pressures,-th'ei'eby permitting: the-use oflighter chamberwallssand generally of' a' lower factor of safety inmotordesigns 'lhlrningmow to the-effect of temperature on the burning: rate,a low dependence of the burning rate on' the temperature of the fuelprior to ignition (referred to as ambient or pr'e-ignition temperature)is of the ut mostl importance in rocket design, for several reasons. Inthe first.place,-if thefuel has a large temperature co'- eflicient of-pressure-(it e., rate of:change.0f pressure with respect topre-ignition temperature, in a given motor using: a grainrofgiven-area Aa motorthat is safe to meat low pre-ignitiontemperatures may burst ifused; for example under hotdesert conditions. On the other hand, if themotor is designecl-for useat highpreignition temperatures, then it isunnecessarily massive for use under moderate or low temperatureconditions; Furthermore, .ifthe pressure developed'in the rocket motorfalls: below a certain-threshold value, the propellant tends to burnincompletely; Therefore, if the fuelis characten' izedby alargetemperature, coefiicient, the possibility is increased of burn-outs" atlow pre-ignition temperatures; aswell as fblow-outs at high-pre-ignitiontemperatures. Finally, a fuel with a large temperature coefficient willbe characterized by an undesirably high degree of dispersion at lowpre-ignition temperatures, and also by variable ballistics (changes inrange) with variations in: the temperature of the fuel-prior toignition.

Considering the temperature factor somewhat more closely, ithas beenfound that if the rate of burningis measured at different ambienttemperatures but at the-- same maximum pressure, then the rate of changeof burning with temperatureisrelativeIy small in the case ofpractically, all existing: rocket fuels. Unfortunately, how ever, inactual use,'the only factor capable of being main tained substantiallyconstantris the. ratio: A /A i. e., the grain area and the throat area.In other words, the maximum pressure developed inthe motor chamber is'not a constant butrvaries with the ambient temperature. But aspreviously, explained, in-the-case of fuels-having a large value of: n,changes. inpressure profoundly affect the rate of'buruing. Accordingly,thetemperature effect is intimately related to. thepressurevefiect.

The temperature effect discussed above is more pre cisely defined by therelation:

value of the exponential constant 11,. the smaller will bethetemperaturecoefficient of" the rate of burning at a constant A' to A ratio.Conversely, if n approaches unity, the temperature coefficient of the.burning rate From the foregoing, it will be apparent that a small valueof the exponential constant n in the so-called burnand 1 isthe'dilference'betweenthesquare-and cube-of a very large numhenlforinstance,.the difference between t (200 and- (200) which intthis caseamounts to 7,960,000.- Small numerical diifere'ncesin n values ofimpulse fuels are, accordingly,.of great significance, not only. inrespectto' reproducibility at a substantially constant preignitiontemperature, but also withrespect to uniformity of action under;varying" pre ignition temperatures.

Inthe preceding paragraphs, the importance-of (1 )a smallzdeviation fromthe burning-l law, (2) a small 11 value, and (3)aloW-temperature-coetficient, have been discussed. In additiontothesefactors itis also, desirable Y to employ apropellantcharacterizedby. as high a density as possible, inasmuchasahighdensity permits-the use of. a smaller firing chamber, therebymaking itpo ssibleto decreasei the'sizeand mass of the motor andtherefore to improve thetballistics of the'motor.

From-the'above analysis it will;be apparent that the design oftheimpulse fuehpresents an exceedingly complex problem, the solution ofwhich is-complicated bythe l fact that the properties of a gasgenerating composition under atmospheric conditionsafford practically noindication ofthe properties of such composition. when burned under theconditions obtaining in an impulsemotore In short, the design-0fapropellant fuel for jet propulsion at the present:: time isalmostentirely an empirical problem, that requires. the mostpainstakingand protractedexperimentation. A

Broadly; speaking, the object= ofthe present invention isto'provid'eanew andimproved gas generating compositionsuitable for. rocketpurposes.

A more particular object is the provision of a novel impulse propellantcharacterized by z (1) A burning rate which deviates only'slightly fromthe so-c'alled burning law";

(2) A low value of the exp'onnentialconstant ll in the burning 1 law;

(3-) A" low temperature coefficient of pressure change when: afuel ofgiven'grain area is fired'in'a given'rnotor at variouspre-ignitiontemperatures. A further object'isap'ropellant possessing thefollow ing additional characteristicsz (a) A sufficiently high specificimpulse; (b)- Relatively constant external ballistics;

, (c) A burning-rate whichrnay be made high or low at will;

(d) Adaptability to. the production of grains of high and low burningtimes;

(a) High mechanical strength and freedom from distortion under stress;(I) High loading-density;

(g) Moderate motor. chamber requirements; (h) Adaptability to molding toclose dimensional tolerances without mechanical finishing operations;

(i) Ready. availability. of raw materials,

(j).- Relative simplicity of the equipment required for fabrication.

Other objects and advantages will become apparent as the invention ishereinafter more particularly described.

As the result of an extended investigation it has been found that theobjects set forth above may be obtained by a novel type of propellantconsisting of a particulate gas generating composition compacted in thepresence of a binder comprising a chlorinated polyphenyl body. Moreparticularly, the gas generating composition herein provided consistsessentially of two components; namely, (1) a particulate non-plastic gasgenerating composition and (2) a binder comprising a resinouschlorinated diphenyl or terphenyl with or without one or more resinousbodies. Propellants of the present type differ fundamentally fromprevious fuels of the smokeless powder (ballistite) type wherein theplastic component of the composition was a major constituent. In thecomposite fuels of the present invention the solid non-plastic gasgenerating component constitutes generally as high as 90-95% of thecomposition, the plastic component being employed in relatively smallproportions which serves not only asa binder but as a modifier of theburning characteristics of the gas generating component.

I. THE GAS GENERATING COMPONENT 'The gas generating component inaccordance with the present invention consists of a mixture of finelydivided solid materials which are capable of interaction under theinfluence of heat to produce a-large volume of gaseous reactionproducts. Mixtures of this type usually consists of an oxidizingsubstance and an oxidizable substance. The oxidizing substance maycomprise one or more solid inorganic oxidizing agents such as thenitrates, for example, sodium nitrate, potassium nitrate, bariumnitrate, ammonium nitrate and the like. The oxidizable substancedesirably comprises one or more solid organic nitro compounds or theirsalts, such as the sodium or preferably the ammonium salts of nitrophenols (for example, ammonium picrate) or one or more solid nitramines(for example, nitroguanidine).

In general, the oxidizable substance and the oxidizing substance may beemployed in a wide range of proportions, depending on the particular useto which the ultimate fuel is to be put. In some instances, it may bedesirable to use the components in the proportions required for oxygenbalance for the production of CO and H (i. e., zero oxygen balance); inthe case of ammonium picrate=sodium nitrate mixtures this result isobtained with a weight ratio of 52.5 to 47.5, respectively. However, forother purposes, a different specific impulse or a different burning ratemay be desirable, in which case the relative proportions of componentsmay be considerably altered with a View to modifying one or moreproperties of the fuel. Thus, for aircraft take-off purposes or forother uses where a low rate of burning is desirable, a -90 sodiumnitrate=ammonium picrate composition may be satisfactory, whereas foranti-aircraft rockets or other purposes where a high rate of burning isdesirable a 50-50 mixture of these same components may be preferable.

Generally speaking, in the case of ammonium picratepot'assium nitratemixtures, it is undesirable to employ in excess of about 55% potassiumnitrate, since a further increase in this component increases the solidreaction product (potassium carbonate) at the expense of the gaseousproducts, thereby cutting down the power of the propellant. A highspecific impulse will be obtained with mixtures containing from about10% to about 55% potassium nitrate. A high rate of burning will beobtained with a composition containing ammonium picrate 45%, potassiumnitrate 55%.

Certain general principles governing the relation of composition toimpulse are reasonably clear. Any change in composition which lowers theproportion of solid reaction product tends to increase the specificimpulse, in any case more'than compensating for an accompanying decreasein heat of reaction. Thus, an increase in the proportion of ammoniumpicrate in a mixture with potassium nitrate beyond the 48.5% requiredfor a zero oxygen balance leads to a decrease in the predicted heat of,This general observation serves as auseful guide in devising newproportions of ingredients.

In some cases, it may be desirable to incorporate small amounts of othermaterials in the gas generating composition, in order to modify one ormore characteristics of the molding powder or of the finishedpropellant. Thus, a small amount of a readily combustible material suchas aluminum powder, charcoal, sulfur and the like, may

' be added for the purpose of modifying the burningpropphenol-formaldehyde or urea-formaldehyde resins.

. include a solvent'for, these resins.

erties of the fuel.

II. THE BINDER The chlorinated polyphenyl products mentioned above,which may be used as binders in accordance with the present invention,may comprise the chlorinated diphenyls or chlorinated terphenyls andmixtures thereof. Chlorinated polyphenyls suitable as binders for theproduction of the composite gas generating body may be prepared asdescribed by Jenkins et al., in United States Patent 1,892,400. Whendiphenyl, alone, is chlorinated, the chlorine content should be at least54% by weight and may be as high as 64% or 65% by weight. These productsare preferably used in the non-crystalline form as described in theabove patent; however, some crystalline phase resulting from a somewhathigher degree of chlorination may also be present. As described in theabove mentioned Jenkins et al. patent some higher boiling aromatichydrocarbons related to diphenyl (and comprising the terphenyls) mayalso be present in the material undergoing chlorination. As a matter offact, for the present purpose, the binder may comprise wholly thechlorinated terphenyl fraction, but generally it appearsdesirable toemploy a mixture of diphenyl and terphenyl as the hydrocarbonwhich ischlorinated, to the extent of between 40% and 60% or 65% by weight ofchlorine. For the purpose of the present specification and claims, thechlorinated diphenyl and/ or teiphenyl product is referred to aschlorinated polyphenyl.

While the chlorinated diphenyls and/er terphenyls may be used alone asthe binder and burning rate modifier, for certain purposes it maybedesirable to incorporate additional resinous compounds therewith forthe purpose of increasing the tack and strength of the binder. For thispurpose, I may use any resinous materials such as The phenolicconstituent of these phenol-formaldehyde resins may be ordinary phenol,cresol, para-phenyl phenol or tertiary butyl phenol. These resins areemployed in the heat-reactive condition so that upon heating, which maytake place at a lower temperature, they become infusible and insoluble.When oil-soluble phenolic resins such as the para-phenylphenol-formaldehyde or tertiary butyl phenol-formaldehyde resins areemployed, the binder may These solvents may be drying oil such as tungor linseed oil. Phenol-formaldehyde resins in the B stage are soluble inalcohol and may be added while dissolved in this type of solvent.

On the other hand, urea-formaldehyde resins in theheatreactive statemaybe employed as solutions in toluene; xylene and butanol. These resinsmay be prepared as d'eescribed' in Uhited- StatesPatent No. 2,171,882,issued September 5, 1939.

The binder is incorporated into the gas generating compositionby simplemixing'withthe gas forming materials. If the mixture of gas'formingmaterial and binder is rolled upon slightly heated rolls for afew minutes; a more intimate mixing of the ingredients is obtained.Where a solvent is present inthe bindercompositiomthe material may alsoberolled upon cold rolls. Pigment rolls such as areemployed in thepaintindustry may be'used.

During rolling, any'solvent present in theresinous binder is" readilyevaporated and the operation of rolling desirably should be continueduntil' a. dry, powdery material free of solvent is obtained.

In order to avoid adversely affecting the internal'ballistics of thepropellant, a restricted amount of resinous bindershould be employed;namely, an amount of resin merely sufiicientto enable the production ofthe mechanically strong grain to be achieved. Usually from 5% to 10% byweight of resin 'mthe finished grain is suflicient to obtain the desiredmechanical properties without adversely affecting the burningcharacteristics ofthe composition. In some cases, as little as 3% ofresin as binder may be satisfactory.

III. COMPOUNDING THE INGREDIENTS In producing the composite propellantof the present invention the oxidizing component (for example, potassiumnitrate) is preferably first dried and then ground to a finely dividedcondition. The powdered oxidizable component (for example, ammoniumpicrate) is mixed with the oxidizing agent, the former likewise being ina finely powdered condition; 'The chlorinated polyphenyl binder with orwithout aflresinous binder is next added and thoroughly incorporatedtherewith. As stated above,

grain is desirably cured at a temperature sufficient to render the resininsoluble and infusible. Temperatures between 30 C. and 80 C. may beemployed for curing the resin. Condensation catalysts may be present in.the composition in order to accelerate the curing reactions.

IV. CEMENTING AND' COATING THE GRAINS Because of the powdery nature ofthe composition resulting from the incorporation of the resinous binderwith the solid gas generating ingredients an inherently high degree ofinternal friction in the pressing operation renders it difiicult to moldvery low grains. Where such long grains are desired, a plurality ofshort, readily molded grains may be cementedtogether by means of anysuitable cement containing thermosetting resins such as alkyd resins,etc., the resulting composite fabricated grains exhibiting excellentproperties, as will be herein after described. l

For many jet propulsion applications. it is of considerable advantagetobe able to restrict the burning ofthe fuel body to certain parts of its:surface, either for the purpose of producing a-grain of neutral burningarea, or

for the purpose ofrestr icting. the burning of the grain to a particulararea of the grain. The compositions of the mesh standard screen size.

.present invention are particularly adapted to the formation of such.restricted burning; grains inasmuch as the binder will not ditfuse intoand" adversely affect coating materials designed to prevent burning oncertain parts of the surface. I

As the result of an extensive survey, it has been found that practicallyanystandard varnish" or' paint containing either a" drying oil such aslinseedv oil or an alkyd resin produces an excellent flame-resistingcoating Thus a large variety of paintsand varnishes including standardspar varnish, automobile paint, barn and :roof paint; asphalt varnishand many other types of available coat ing material maybeused'asflame-resistingcoatings'. The coating materials may be convenientlyapplied totthei grains by painting, sprayingor dipping, followed'by drying in. any manner. suited to thecharacter of the applied coating.Thereafter the coated surface may be additionally protected by means ofadhesive textile tapes out by other suitable means. Such coatings havebeen found to withstand pressures well over Z000 lbs./in.

v. EXAMPLE In order. more clearly to disclose the nature of the presentinvention,. a preferredvembodiment will nowbe described in considerabledetail. It should be clearly understood, however, that this is donesolelyfor the purpose of. illustrating the principle of the inventionlay-means of a concreteexample. Accordingly,.the followingdetaileddescription. is not-to be construed as a' limitation upon the spirit orscope of theinvention whichis more particularly defined in the. appendedclaims. K

In producing the preferred gas generating composition: of the present.invention, commercially pure potassium nitrate is first dried to" lessthan i of water, them ground to a particlegsize preferably to 70% 'minus3251 The dry, powdered potasw sium nitrate is thoroughly mixedwithfinely precipitated: ammoniumpicratein-the proportionof 55:45 byweight.

A: nomcrystalline; chlorinatedpolyphenyl resin suchrase is described inExample VI: ofUnitedStates Patentt1,892;a- 400 inpowdered form is mixedtherewith inthepropor tions of parts by Weight of the potassiumnitrate-ammonium picrate mixture to 10'parts by weight of chlo= rinated.polyphenyl resin. The. powdery mixture is thenincorporated on heatedrolls forr'a few minutes; At the:

completion of'rolling, the. material is allowed to'cool -and then againfinely powdered. The powder so produced'is formed into agrainby'pressingin aheated die.

Thegrains are now ready for use either as formed or after cementingseveral grains together to-form a larger grain orafter coating with aflame-resisting material to: form restricted burning grains." Cementingmay he conveniently carried out by applying a thin coat of co ment(alkyd resins such as Glyp tal 1201) to thesurfaces to be joined,pressing the two surfaces together and maintaining a light pressure onthe joined portions during the curing operation. Restricted burninggrains may be pro duced by spraying a selected area such as the ends ofa perforated cylindrical grain if neutral burning is required, or thesides and one end of a large, solid, cylindrical grain with anycommercial coating material. containing. linseed oil or an alkyd resinThe coated surf-acetmay be additionally protected by applying anadhesive coated: fabric tape over the resin coating.

VI. PROPERTIES OF THE' COMPOSITE PROPELLANT Table I1 summarizes. theballistically importantt DIOR" erties of the two specific compositionsin accordance'withw the present invention. For purposes of comparisonthe corresponding data on ballistite are also given.

varied over a wide range.

1 The composition listed as C. P.1, contained the following ingredientsin percent by weight: 45% NaNO 45% ammonium picrate and 10% of achlorinated diphenyl-polyphenyl resin.

The composition listed as C. P.-2, contained the following ingredientsin percent by weight: 47% NaNOa, 47% ammonium picrate, 4.3% of aurea-formaldehyde resin and 1.7% of a chlorinated diphenyl resin. 1

From the foregoing data it will be apparent that the compositepropellant of the present invention is characterized by the followingadvantageous properties:

1) The material has highly reproducible ballistics. The logrithmic plotof pressures against A /A is a straight line over the range of from1,000 to 4,000 p. s. i.

(2) The linear rate of burning of the present trials can be varied overa wide range. This may be accomplished by changing either the specificcomposition of the powdery gas generating composition or the specificcomposition of the binder. Thus, the present propellant lends itself toa wide variety of uses requiring entirely different burning rates.

(3) The rate of burning has a low dependence on pressure. Theexponential constant n in the burning law has a value of about 0.4 toabout 0.5, depending on the composition over a pressure range of from500 to 14,000 p. s. i. for grains of neutral burning area. From this itfollows that the pressure in the rocket motor will vary as the 1.7 powerof the A to A ratio. For comparison, the value of u for smokeless powderis about 0.7 and the area-pressure exponent is about 3.7. Because of thelow value of n for the composite propellant of the present invention, amuch smaller change in chamber pressure will result from anyirregularity in burning which causes a change in the burning area orfrom variations in orifice or throat area. Furthermore, the low it valueinsures a lower pressure drop along a long grain than in the case ofsmokeless powder. Together with the high reproducibility of the chamberpressure, it permits the use of lighter chamber Walls and generally alower factor of safety in motor design.

(4) The rate of burning has a low dependence on temperature. In the caseof the present fuels, over the range from 40 to +60 C., the pressureincreases only about 0.50% for each degree centigrade rise intemperature. For smokeless powder the corresponding figure appears to beof the orderof 15%, per 10 C.

(5) The value of K (i. e., A to A ratio) may be This may be accomplishedby modifying the specific composition of the grain.

(6) The specific impulse is satisfactorily high (of the order of 160-170for optimum expansion ratio).

(7) The composite propellant has a high density (e. g., about 1.75 to1.85 grams per cc.), which permits an appreciably higher load densitythan with smokeless powder (density about 1.63 grams per cc.). Inaddition, the low values of n and K (see items 2 and 4) permit the useof smaller port areas in the motor chamber and this also favors highloading density.

(8) The composite propellant has a high crushing strength (about 5,000to 12,000 p. s. i. depending on the composition) and suffers nosignificant distortion under stresses short of those required forfracture.

(9) It may be molded to close dimensional tolerances and requires nosubstantial amount of finishing by machining operations.

(10) The impact sensitivity of the material is satisfactory(approximately the same as that for ammonium picrate).

(11) The chemical stability of the material is satisfactory as judged bythe usual accelerated tests. The ballistic properties of grains burnedafter storage for several months have been satisfactory in that nochange has taken place. Many grains have been subjected to a temperaturecycle of 8 hours per cycle between +60 C. and 45 C. for 20 cycleswithout showing any significant change in ballistic properties, indensity, or in compression strength.

(12) The burning of the cemented grains shows no irregularities whateverarising from the composite, builtup or fabricated structure.

(13) The restriction of the burning area by means of protective coatingsis entirely successful. The grains contain no diffusible liquid, such asnitroglycerine, which has caused so much trouble in attempts to restrictburning of double base powder grains.

What I claim is:

i. A composite jet propulsion propellant essentially composed of adense, compact mixture of crystalline particles of ammonium picrate andparticles of a crystalline inorganic nitrate selected from the classconsisting of sodium nitrate, potassium nitrate, barium nitrate andammonium nitrate, said mixture containing between 10% and 55% of saidnitrate, the balance of said mixture being particles of ammonium picrateand from 5% to 10% of a resinous matrix for said particles, said matrixconsisting of a material selected from the class consisting of resinouschlorinated polyphenyls containing at least 40% of chlorine and mixturesof chlorinated polyphenyls containing at least 40% chlorine with aurea-formaldehyde resin.

2. A composite jet propulsion propellant essentially composed of adense, compact mixture of crystalline particles of ammonium picrate andpotassium nitrate, said mixture containing between 10% and 55% of saidnitrate and the balance thereof being ammonium picrate and from 5% to10% of said mixture of a resinous matrix for said particles, said matrixconsisting of a chlorinated polyphenyl containing between 42% and 65% byweight of chlorine.

3. A composite jet propulsion propellant essentially composed of adense, compact mixture of crystalline particles of ammonium picrate andvpotassium nitrate, said mixture containing between 10% and 55% of saidnitrate and the balance thereof being ammonium picrate and from 5% to10% of said mixture of a resinous matrix for said particles, said matrixconsisting of a chlorinated polyphenyl resin containing between 42% and65% by weight of chlorine, said propellant having a density of 1.92.

4. A composite jet propulsion propellant essentially composed of adense, compact mixture of crystalline particles of ammonium picrate andpotassium nitrate, said mixture containing between 10% and 55% of saidnitrate and the balance thereof being ammonium picrate and from 5% to10% of said mixture of a resinous matrix for said particles, said matrixconsisting of a mixture of a urea-formaldehyde resin and a chlorinatedpolyphenyl resin containing between 42% and 65% by weight of chlorine,said propellant having a density of 1.79.

5. A composite jet propulsion propellant essentially composed of adense, compact mixture of crystalline particles of ammonium picrate andsodium nitrate, said mixture containing 45% sodium nitrate, 45 ofammonium picrate and a resinous matrix for said particles, said matrixconsisting of 10% of a chlorinated polyphenyl resin containing between42% and 65% of chlorine.

6. A composite jet propulsion propellant essentially composed of adense, compact mixture of crystalline particles of ammonium picrate andsodium nitrate, said mixture containing 47% of sodium nitrate and 47% ofammonium picrate and a resinous matrix for said parti- 1 .1 120123;.8311?matliiXLCOnSiSTing of 413%" ofimurfimfbrmalder 2,409,111Davis Oct. 8, 1946 hyde resin and 1.7% of a chlorinatedpolyphenylzresinw 2,433,417 Bitting et a1 Dec. 30, 1947centaini'ngzbetween; 42%: andi 65%: Off chlorine; 2,434,872 T-aylbr Jim.20} 1948 Referenceszfiitedin'thezfila'ofthis patent w 1 PATENTS 4 UNITEDSTATES PATENTS 6,258 Great Britain A.D,,1892

363,-224 Gerhard- May 17 ;,18 87 9,062 Great'Biitain DJ 1899 1,892,400Jenkins Dec. 27, 1932 21,529 Great, Britain A.: D; 1905' 1,975,072 BoothOct. 2, 19 34 10, 338,848 Germany "July 4; 1921- 2,159,234 Taylor May23,1939 1 9 2,165,263 Holm Q ,Ju1y11, 1939' OTHER REFERENCES 4 4 195 955Helm Apn 1 4 Penning: Chlorinated Diphenyl, Ind: andEng,

2,3 5,170 Bitting -,19, 19 4, Chem.,November 1930, pages 1180iand 1:182.

- UNITED STATES PATENT OFFICE CERTIFIQATE 0F CQRREC'HUN Pater-r- No 2,857,25

Bomber 21, 1958 It is hereby certified that error appears in the printedspecification of the above numbered patent requiring correct-ion andthat the said Letters Patent should readas corrected below.

Colman l, 76, for "depedence", occurrence, read depe ems column line 1,for "unit" read we unity column 7, line 42, for "thermos-Easting"thermcse' ating line 62, for "low" read long Signed 31st of May 1960(SEAL) fittest:

143mm ROBERT C. WATSON Attesting Officer Commissioner of Patents UNITEDSTATES PATENT OFFICE CERHFMATE @F QQRRE CHQN Patent Nou 2,857,125.

Gctober 21, 1958 12L "I r1 v (Juli-Tries A, Thomas It is herebycertified that error appears in the printed specification of the abovenumbered patent requiring correction and that the said Letters Patentshould readas corrected below.

6011mm. 1, line 7 3, s d column 2, 28, de-pedence each occurrence, readenc'e ===3 column 3, iirie' l, for "unit read w unity 5 column "7, 42;,for "thermostat =thermosetting 62, for New" m long we Signed 31st of May1960 (SEAL) fittest:

KARL AXLTTTE ROBERT C. WATSON Arresting Ufiicer fiommissioner of Patents

1. A COMPOSITE JET PROPULSION PROPELLANT ESSENTIALLY COMPOSED OF ADENSE, COMPACT MIXTURE OF CRYSTALLINE PARTICLES OF AMMONIUM PICRATE ANDPARTICLES OF A CRYSTALLINE INORGANIC NITRATE SELECTED FROM THE CLASSCONSISTING OF SODIUM PITRATE, POTASSIUM NITRATE, BARIUM NITRATE ANDAMMONIUM NITRATE, SAID MIXTURE CONTAINING BETWEEN 10% AND 55% OF SAIDNITRATE, THE BALANCE OF SAID MIXTURE BEING PARTICLES OF AMMONIUM PICRATEAND FROM 5% TO 10% OF A RESINOUS MATRIX FOR SAID PARTICLES, SAID MATRIXCONSISTING OF A MATERIAL SELECTED FROM THE CLASS CONSISTING OF RESINOUSCHLORINATED POLYPHENYLS CONTAINING AT LEAST 40% OF CHLORINE AND MIXTURESOF CHLORINATED POLYPHENYLS CONTAINING AT LEAST 40% CHLORINE WITH AUREA-FORMALDEHYDE RESIN.